From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D4B20C432C0 for ; Fri, 29 Nov 2019 08:30:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A7A8221774 for ; Fri, 29 Nov 2019 08:30:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726888AbfK2IaN (ORCPT ); Fri, 29 Nov 2019 03:30:13 -0500 Received: from mga03.intel.com ([134.134.136.65]:36760 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725892AbfK2IaN (ORCPT ); Fri, 29 Nov 2019 03:30:13 -0500 X-Amp-Result: UNKNOWN X-Amp-Original-Verdict: FILE UNKNOWN X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 29 Nov 2019 00:30:12 -0800 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.69,256,1571727600"; d="scan'208";a="234645172" Received: from richard.sh.intel.com (HELO localhost) ([10.239.159.54]) by fmsmga004.fm.intel.com with ESMTP; 29 Nov 2019 00:30:10 -0800 Date: Fri, 29 Nov 2019 16:30:02 +0800 From: Wei Yang To: Matthew Wilcox Cc: Wei Yang , "Kirill A. Shutemov" , Wei Yang , akpm@linux-foundation.org, kirill.shutemov@linux.intel.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm/page_vma_mapped: page table boundary is already guaranteed Message-ID: <20191129083002.GA1669@richard> Reply-To: Wei Yang References: <20191128010321.21730-1-richardw.yang@linux.intel.com> <20191128010321.21730-2-richardw.yang@linux.intel.com> <20191128083143.kwih655snxqa2qnm@box.shutemov.name> <20191128210945.6gtt7wlygsvxip4n@master> <20191128223904.GG20752@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191128223904.GG20752@bombadil.infradead.org> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 28, 2019 at 02:39:04PM -0800, Matthew Wilcox wrote: >On Thu, Nov 28, 2019 at 09:09:45PM +0000, Wei Yang wrote: >> On Thu, Nov 28, 2019 at 11:31:43AM +0300, Kirill A. Shutemov wrote: >> >On Thu, Nov 28, 2019 at 09:03:21AM +0800, Wei Yang wrote: >> >> The check here is to guarantee pvmw->address iteration is limited in one >> >> page table boundary. To be specific, here the address range should be in >> >> one PMD_SIZE. >> >> >> >> If my understanding is correct, this check is already done in the above >> >> check: >> >> >> >> address >= __vma_address(page, vma) + PMD_SIZE >> >> >> >> The boundary check here seems not necessary. >> >> >> >> Signed-off-by: Wei Yang >> > >> >NAK. >> > >> >THP can be mapped with PTE not aligned to PMD_SIZE. Consider mremap(). >> > >> >> Hi, Kirill >> >> Thanks for your comment during Thanks Giving Day. Happy holiday:-) >> >> I didn't think about this case before, thanks for reminding. Then I tried to >> understand your concern. >> >> mremap() would expand/shrink a memory mapping. In this case, probably shrink >> is in concern. Since pvmw->page and pvmw->vma are not changed in the loop, the >> case you mentioned maybe pvmw->page is the head of a THP but part of it is >> unmapped. > >mremap() can also move a mapping, see MREMAP_FIXED. Hi, Matthew Thanks for your comment. I took a look into the MREMAP_FIXED case, but still not clear in which case it fall into the situation Kirill mentioned. Per my understanding, move mapping is achieved in two steps: * unmap some range in old vma if old_len >= new_len * move vma If the length doesn't change, we are expecting to have the "copy" of old vma. This doesn't change the THP PMD mapping. So the change still happens in the unmap step, if I am correct. Would you mind giving me more hint on the case when we would have the situation as Kirill mentioned? > >> This means the following condition stands: >> >> vma->vm_start <= vma_address(page) >> vma->vm_end <= vma_address(page) + page_size(page) >> >> Since we have checked address with vm_end, do you think this case is also >> guarded? >> >> Not sure my understanding is correct, look forward your comments. >> >> >> Test: >> >> more than 48 hours kernel build test shows this code is not touched. >> > >> >Not an argument. I doubt mremap(2) is ever called in kernel build >> >workload. >> > >> >-- >> > Kirill A. Shutemov >> >> -- >> Wei Yang >> Help you, Help me >> -- Wei Yang Help you, Help me